After getting a lot of helpful feedback I've arrived at a question:

What if we setup base on Mars:

I) Mine water, and split it for propellant. II) Load up light weight (expandable?) rockets with it. III) Send them in-ward towards an asteroid belt. IV) Capture asteroids and tug them to earth orbit V) If possible, setup a space elevator to slingshot rockets to asteroids.

Would the speed difference (with an asteroid) of a rocket launched from Mars (vs a rocket slingshot back around Jupiter) be small enough to successfully capture an asteroid?

  • $\begingroup$ Do you mean Mars in general, or the specific plan outlined in your question? $\endgroup$
    – Topcode
    Commented Sep 6, 2022 at 1:56
  • $\begingroup$ Definitely in general - my ideas keep on evolving as I get more replies from experts. I'm incredibly grateful for the distilled knowledge coming my way in such a short period of time. It lets a layman (with a goal like mine) pursue his quest for truth without being stopped by the present realities of the situation. Thank you! :) $\endgroup$ Commented Sep 6, 2022 at 4:20
  • $\begingroup$ Added a related "thought seed" here: space.stackexchange.com/questions/60250/… ;^) $\endgroup$ Commented Sep 6, 2022 at 4:46
  • $\begingroup$ What use is Mars? That is: you are paying a lot in δv to get down to it and up again. What are you buying? From what you’ve said, it sounds like just ice, which is surely available elsewhere with less gravity cost. But perhaps there are other advantages of a planetary surface which you haven’t mentioned. $\endgroup$ Commented Sep 6, 2022 at 7:48
  • $\begingroup$ Mars is useful. There's two asteroid-like moons in orbit that would make wonderful laboratories for asteroid mining R&D, just hours and a couple km/s away from a surface with abundant natural resources and a more human-friendly environment. And the main belt is relatively easy to reach from a spacecraft reloaded with propellant in Mars orbit. You just wouldn't use this capability to ship propellant to the asteroids for moving them to Earth, as the question suggests. $\endgroup$ Commented Sep 8, 2022 at 18:03

2 Answers 2

  1. The main benefit of Mars for asteroid mining would be for accessing asteroids that are further out, not ones that are closer to Earth than Mars itself.
  2. Transporting propellant from anywhere else to an asteroid for moving that asteroid is likely a losing game. If you use hydrolox propellant and have engines with 465 s specific impulse, you'll need twice as much propellant as asteroid to achieve 5 km/s of delta-v. That's the propellant delivered to the asteroid. If you need 5 km/s to get it there, your propellant tanker needs to depart for the asteroid with a total of six asteroid masses of propellant.
  3. Asteroids are largely oxygen. Even metallic asteroids have large quantities of silicate minerals containing lots of oxygen. There's no solid object in the solar system which is short on oxygen. Much of the remainder is silicon, magnesium, and other similarly abundant materials. You will find uses for some of these, but you won't want to haul them across the solar system.

If you're moving asteroids at all, it makes more sense to use the unwanted fractions of the asteroid itself as propellant. And considering that a decent-sized asteroid is likely to out-mass the equipment for processing it by many, many times, it really makes sense to process it on-site and transport only the extracted materials that you need.

  • $\begingroup$ Thank you for adding the additional information. I now understand that there isn't much commercial viability to asteroid mining at this point. $\endgroup$ Commented Sep 6, 2022 at 18:59

If you can build a space elevator then you've just removed any need to use Mars or anywhere else other than Earth as a base for exploration/exploitation. With the massive cost of lifting materials to orbit reduced it makes sense to build things where you have food, water, air, radiation shielding and all that other good stuff. Using the Moon or Mars as a base only makes sense if the costs of contending with gravity are more than the costs of building and sustaining a base on another celestial body.

Presuming there's still benefit, as far as can be seen now there's nothing going for Mars as a base for exploiting the resources of the solar system compared to the Moon. The moon is closer and much easier to get to and has lower gravity than Mars which makes landing and launching less expensive. Both have few resources and we don't yet know whether there is water that can be exploited in either location, or how we would use it.

The solar system subway map is a great way to illustrate why Mars doesn't make a great base for exploring/exploiting compared to the moon as it shows the delta-V you need for each leg of a journey from one body to another.

enter image description here

Getting from the surface to the Earth to LEO is 9400m/s, then escaping Earth's gravity takes an additional 3210m/s, from there to get to another body takes whatever delta-v it says to its intercept. So to get from the surface of the Earth to escape velocity is 12610m/s. For Mars it is 5240 and for the Moon a mere 2410m/s. To get from Moon intercept or Earth intercept to other objects takes the same delta-v, and I'm going to assume 2600m/s from Moon/Earth intercept to the asteroid belt as it's half-way between Mars and Jupiter (an oversimplification but it works in this case). Using that figure it's 5010m/s to get from surface of the Moon to the asteroid belt, From Mars I'm going to assume 1300m/s delta-v from Mars intercept to the asteroid belt, so it would be 6540m/s.

So looking at the delta-v figures it's cheaper to launch from the Moon. It's also much, much easier and cheaper to get equipment, supplies and personnel to the Moon.

In many ways Mars really only makes sense from a redundancy perspective, a self-sustaining colony on Mars would save the human race from extinction in the case of a cataclysm on Earth.

  • $\begingroup$ Got it, thank you sir, I greatly appreciate the effort you (and the community) are putting in to answering this (and many other) layman question(s)! I know that (at least) for me it really clears things up when an expert provides a clear picture. It helps me stay focused on the things that really matter, here on Earth. :) $\endgroup$ Commented Sep 6, 2022 at 15:50

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